Future spread of HIV will be drug-resistant strains
Model based on frequency of transmissions
In a collaboration that includes researchers from California and the United Kingdom, a recent study predicts that people who are newly infected with drug-resistant virus will be the major source of new resistant infections.1
"We wished to explore the underlying causes of drug resistance, and made use of retrospective clinical data," says Andrew Leigh Brown, PhD, a visiting professor at the University of California - San Diego and a chief author of the study. Brown also is a professor at the University of Edinburgh in Scotland.
Investigators observed drug resistance among a cohort of HIV patients in San Diego. They found that drug resistance existed in a little more than 20% of newly infected individuals between 1998 and 2000, Leigh Brown says. As part of their investigation into discovering new transmission routes of drug resistance, the researchers compared those who were infected with a drug-resistant virus to those who were not, Leigh Brown says. "We are developing and refining a model to make a more accurate projection of where and how this epidemic will develop," he says.
The investigators found that patients with acquired resistance harbor both wild-type and resistant strains, and either may be transmitted, whereas people harboring a transmitted resistance strain can transmit only resistant strains until a revertant arises. This finding led them to surmise that transmitted drug resistance will continue to increase, which means interventions to prevent transmission are more important than ever before.
"It happens very infrequently that people are dually infected with different strains," Leigh Brown says. "We know this has to be the case, because worldwide there’s a very large recombinance between subtypes, and these could only arise if an individual is dually infected with two subtypes." No one knows how frequently this occurs, because dually infected individuals are difficult to identify. "We had a single case where we observed an individual who was infected with two different strains, and our interpretation was that he was dually infected at roughly the same time," Leigh Brown says. "Our interest in that case was because one strain was multidrug-resistant, and the other was not."
Researchers hypothesized that the patient was infected initially with the drug-resistant strain and later acquired the drug-sensitive strain, which was the same subtype but a different strain, Leigh Brown says.
Eventually, investigators expect to develop a clinically relevant model that will be available for use with observations and data on frequency of transmissions and prevalence of drug resistance. This information may aid clinicians in deciding the best course of treatment for a particular patient, Leigh Brown says. "Previously published models of drug-resistant HIV epidemics have been primarily fundamentally theoretical models that identified possible outcomes," Leigh Brown explains. "We’re trying to develop a clinically based model that will allow us to project the likely outcome."
Reference
1. Leigh Brown AJ, Frost SDW, Mathews WC, et al. Will transmission of drug resistant HIV be driven by individuals infected with drug resistant strains? Presented at the 9th Conference on Retroviruses and Opportunistic Infections. Seattle; Feb. 24-28, 2002. Poster 367-M.
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